<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="./main.css">
    <style>
        .container {
            width: 200px;
            height: 200px;
            outline: 1px solid red;
            display: flex;
            justify-content: center;
            align-items: center;
        }
        .container .box {
            background-color: green;
            width: 100px;
            height: 100px;
        }
        .container .box:hover {
            background-color: blue;
        }
    </style>
</head>
<body>
    <div class="container">
        <div class="box"></div>
    </div>
</body>
</html>